The present invention relates, in general, to implantable medical devices, and, in particular, to new and useful bioabsorbable medical devices that are capable of achieving a desired mass loss through accelerated degradation after the medical device has achieved its desired functional effect or achieved the end of its functional purpose or useful life.
It is widely accepted that polymers have found very relevant and practical uses in the medical field. Thus, the very instability of these polymers, which lead to biodegradation, has proven to be immensely important in medical applications over the last number of decades.
For example, polymers prepared from glycolic acid and lactic acid have found a multitude of uses in the medical industry, beginning with the biodegradable sutures first approved in the 1960's. Since that time, diverse products based on lactic and glycolic acid—and on other materials, including poly(dioxanone), poly(trimethylene carbonate) copolymers, and poly(ε-caprolactone) homopolymers and copolymers—have been accepted for use as medical devices. In addition to these approved devices, a great deal of research continues on polyanhydrides, polyorthoesters, polyphosphazenes, and other biodegradable polymers.
There are a number of reasons as to why a medical practitioner desires a medical device made of a material that degrades. And, the most basic reason begins with the physician's simple desire to have a device that can be used as an implant and will not require a second surgical intervention for removal. Besides eliminating the need for a second surgery, the biodegradation may offer other advantages. For example, a fractured bone that has been fixated with a rigid, nonbiodegradable stainless steel implant has a tendency for refracture upon removal of the implant. Because the stress is borne by the rigid stainless steel, the bone has not been able to carry sufficient load during the healing process.
However, an implant prepared from biodegradable polymer can be engineered to degrade at a rate that will slowly transfer load to the healing bone. Another exciting use for which biodegradable polymers offer tremendous potential is as the basis for drug delivery, either as a drug delivery system alone or in conjunction to functioning as a medical device.
Bioabsorbable implants are typically made from polymeric materials such as lactone-based polyesters. These bulk eroding materials breakdown over time due to chemical hydrolysis to produce water-soluble, low molecular weight fragments. These fragments are then attacked by enzymes to produce lower molecular weight metabolites.
To date, there have been no known bioabsorbable medical devices that are capable of achieving a desired mass loss through accelerated degradation after the medical device has achieved its desired functional effect or achieved the end of its functional purpose or useful life.